Typically, any number of petrochemical feeds, such as whole crude, light gas oil (LGO), light cycle oil (LCO) and virgin diesel, require removal of heteroatom species. Such heteroatom species include nitrogen-containing and/or sulfur-containing species. For example, hydrotreating is used to lower content of nitrogen-containing and/or or sulfur-containing species from petrochemical feeds (e.g., virgin diesel). However, nitrogen-containing species can poison the hydrotreating catalysts. Thus, high pressure hydrotreating is necessary to overcome nitrogen poisoning of the catalysts and to effectively remove the sulfur-containing species to meet sulfur content specifications of the various feedstreams. Thus, there is a need for an adsorbent which can remove or separate nitrogen-containing species from petrochemical feeds prior to hydrotreating so that hydrotreating may be performed at lower pressures.
Porous inorganic solids have found great utility as separation media for industrial application. In particular, mesoporous materials, such as silicas and aluminas, having a periodic arrangement of mesopores are attractive materials for use in adsorption and separation processes due to their uniform and tunable pores, high surface areas and large pore volumes. Such mesoporous materials are known to have large specific surface areas (e.g., 1000 m2/g) and large pore volumes (e.g., 1 cm3/g). For these reasons, such mesoporous materials enable molecules to rapidly diffuse into the pores and therefore, can be advantageous over zeolites, which have smaller pore sizes. Consequently, such mesoporous materials can be useful as large capacity adsorbents.
However, mesoporous organosilicas, which may be used as adsorbents are conventionally formed by the self-assembly of the silsesquioxane precursor in the presence of a structure directing agent, a porogen and/or a framework element. The precursor is hydrolysable and condenses around the structure directing agent. These materials have been referred to as Periodic Mesoporous Organosilicates (PMOs), due to the presence of periodic arrays of parallel aligned mesoscale channels. For example, Landskron, K., et al. [Science, 302:266-269 (2003)] report the self-assembly of 1,3,5-tris[diethoxysila]cylcohexane [(EtO)2SiCH2]3 in the presence of a base and the structure directing agent, cetyltrimethylammonium bromide to form PMOs that are bridged organosilicas with a periodic mesoporous framework, which consist of SiO3R or SiO2R2 building blocks, where R is a bridging organic group. In PMOs, the organic groups can be homogenously distributed in the pore walls. U.S. Pat. Pub. No. 2012/0059181 reports the preparation of a crystalline hybrid organic-inorganic silicate formed from 1,1,3,3,5,5 hexaethoxy-1,3,5 trisilyl cyclohexane in the presence of NaAlO2 and base. U.S. Patent Application Publication No. 2007/003492 reports preparation of a composition formed from 1,1,3,3,5,5 hexaethoxy-1,3,5 trisilyl cyclohexane in the presence of propylene glycol monomethyl ether.
However, the use of a structure directing agent, such as a surfactant, in the preparation of an organosilica material, requires a complicated, energy intensive process to eliminate the structure directing agent at the end of the preparation process. For example, calcining may be required as well as wastewater disposal steps and associated costs to dispose of the structure directing agent. This limits the ability to scale-up the process for industrial applications.
Therefore, there is a need for improved adsorbents and/or processes for heteroatom species removal or separation from hydrocarbon feeds using organosilica materials that can be prepared by a method that can be practiced in the absence of a structure directing agent, a porogen or surfactant.